Chapter 4 Community Ecology, Population Ecology, and the Human Population

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Chapter 4Community Ecology, Population Ecology,
and the Human Population
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4-1 What Roles Do Species Play in Ecosystems?

• Concept 4-1A Each species plays a specific
  ecological role called its niche.
• Concept 4-1B Any given species may play one or
  more of five important rolesnative, nonnative,
  indicator, keystone, or foundation rolesin a
  particular ecosystem.

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Each Species Plays a Unique Role in Its Ecosystem

• Ecological niche, niche
• Pattern of living everything that affects
  survival and reproduction
• Water, space, sunlight, food, temperatures
• Generalist species
• Broad niche wide range of tolerance
• Specialist species
• Narrow niche narrow range of tolerance

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Specialized Feeding Niches of Various Bird
Species in a Coastal Wetland
Fig. 4-1, p. 68
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Ruddy turnstone searches under shells and
pebbles for small invertebrates
Herring gull is a tireless scavenger
Avocet sweeps bill through mud and surface water
in search of small crustaceans, insects, and seeds
Brown pelican dives for fish, which it locates
from the air
Dowitcher probes deeply into mud in search of
snails, marine worms, and small crustaceans
Black skimmer seizes small fish at water surface
Oystercatcher feeds on clams, mussels, and
other shellfish into which it pries its narrow
beak
Knot (sandpiper) picks up worms and small
crustaceans left by receding tide
Piping plover feeds on insects and
tiny crustaceans on sandy beaches
Flamingo feeds on minute organisms in mud
Scaup and other diving ducks feed on
mollusks, crustaceans, and aquatic vegetation
Louisiana heron wades into water to seize small
fish
Fig. 4-1, p. 68
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Case Study Cockroaches Natures Ultimate
Survivors

• 3500 species
• Generalists
• Eat almost anything
• Live in almost any climate
• High reproductive rates

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Species Can Play Five Major Roles within
Ecosystems

• Native species
• Nonnative species
• Indicator species
• Keystone species
• Foundation species

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Indicator Species Serve as Biological Smoke Alarms

• Indicator species
• Provide early warning of damage to a community
• Can monitor environmental quality
• Trout
• Birds
• Butterflies
• Frogs

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Case Study Why Are Amphibians Vanishing? (1)

• Habitat loss and fragmentation
• Prolonged drought
• Pollution
• Increase in UV radiation
• Parasites
• Viral and fungal diseases
• Climate change
• Overhunting
• Nonnative predators and competitors

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Case Study Why Are Amphibians Vanishing? (2)

• Importance of amphibians
• Sensitive biological indicators of environmental
  changes
• Adult amphibians
• Important ecological roles in biological
  communities
• Genetic storehouse of pharmaceutical products
  waiting to be discovered

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Life Cycle of a Frog
Fig. 4-2, p. 70
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Adult frog (3 years)
Young frog
Sperm
Tadpole develops into frog
Sexual reproduction
Tadpole
Eggs
Fertilized egg development
Egg hatches
Organ formation
Fig. 4-2, p. 70
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Keystone and Foundation Species Play Critical
Roles in Their Ecosystems (1)

• Keystone species roles have a large effect on
  the types and abundances of other species
• Pollinators
• Top predators

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Keystone and Foundation Species Play Critical
Roles in Their Ecosystems (2)

• Foundation species
• Create or enhance their habitats, which benefit
  others
• Elephants
• Beavers

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Case Study Why Should We Protect Sharks?

• 400 known species
• 6 deaths per year from shark attacks
• 79-97 million sharks killed every year
• Fins
• Organs, meat, hides
• Fear
• 32 shark species threatened with extinction
• Keystone species
• Cancer resistant

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4-2 How Do Species Interact?

• Concept 4-2 Five types of species
  interactionscompetition, predation, parasitism,
  mutualism, and commensalismaffect the resource
  use and population sizes of the species in an
  ecosystem.

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Species Interact in Five Major Ways

• Interspecific Competition
• Predation
• Parasitism
• Mutualism
• Commensalism

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Most Species Compete with One Another for Certain
Resources

• For limited resources
• Ecological niche for exploiting resources
• Some niches overlap

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Some Species Evolve Ways to Share Resources

• Resource partitioning
• Using only parts of resource
• Using at different times
• Using in different ways

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Resource Partitioning Among Warblers
Fig. 4-3, p. 73
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Yellow-rumped Warbler
Blackburnian Warbler
Black-throated Green Warbler
Cape May Warbler
Bay-breasted Warbler
Fig. 4-3, p. 73
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Most Consumer Species Feed on Live Organisms of
Other Species

• Predation
• Predators capture prey
• Part of a food web
• Predators play a role in the evolution of prey

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Some Species Feed off Other Species by Living on
or in Them

• Parasitism
• Parasite is usually much smaller than the host
• Parasite rarely kills the host
• Parasite-host interaction may lead to coevolution

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In Some Interactions, Both Species Benefit

• Mutualism
• Nutrition and protection relationship
• Gut inhabitant mutualism
• Not cooperation its mutual exploitation

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Mutualism Oxpeckers Clean Rhinoceros Anemones
Protect and Feed Clownfish
Fig. 4-4, p. 74
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Fig. 4-4a, p. 74
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(a) Oxpeckers and black rhinoceros
Fig. 4-4a, p. 74
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Fig. 4-4b, p. 74
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(b) Clownfish and sea anemone
Fig. 4-4b, p. 74
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In Some Interactions, One Species Benefits and
the Other Is Not Harmed

• Commensalism
• Epiphytes
• Birds nesting in trees

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4-3 How Do Communities and Ecosystems Respond to
Changing Environmental Conditions?

• Concept 4-3 The structure and species
  composition of communities and ecosystems change
  in response to changing environmental conditions
  through a process called ecological succession.

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Communities and Ecosystems Change over Time
Ecological Succession

• Natural ecological restoration
• Primary succession
• Secondary succession

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Some Ecosystems Start from Scratch Primary
Succession

• No soil in a terrestrial system
• No bottom sediment in an aquatic system
• Takes hundreds to thousands of years
• Need to build up soils/sediments to provide
  necessary nutrients

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Primary Ecological Succession
Fig. 4-5, p. 75
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Balsam fir, paper birch, and white spruce forest
community
Jack pine, black spruce, and aspen
Heath mat
Small herbs and shrubs
Lichens and mosses
Exposed rocks
Time
Fig. 4-5, p. 75
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Some Ecosystems Do Not Have to Start from
Scratch Secondary Succession

• Some soil remains in a terrestrial system
• Some bottom sediment remains in an aquatic system
• Ecosystem has been
• Disturbed
• Removed
• Destroyed

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Natural Ecological Restoration of Disturbed Land
Fig. 4-6, p. 76
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Mature oak and hickory forest
Young pine forest with developing understory of
oak and hickory trees
Shrubs and small pine seedlings
Perennial weeds and grasses
Annual weeds
Time
Fig. 4-6, p. 76
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Primary and Secondary Succession Considerations

• Primary and secondary succession
• Tend to increase biodiversity
• Increase species richness and interactions among
  species
• Primary and secondary succession can be
  interrupted by
• Fires
• Hurricanes
• Clear-cutting of forests
• Plowing of grasslands
• Invasion by nonnative species

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Succession Doesnt Follow a Predictable Path

• Traditional view
• Balance of nature and a climax community
• Current view
• Ever-changing mosaic of patches of vegetation
• Mature late-successional ecosystems
• State of continual disturbance and change

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4-4 What Limits the Growth of Populations?

• Concept 4-4 No population can continue to grow
  indefinitely because of limitations on resources
  and because of competition among species for
  those resources.

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Populations Can Grow, Shrink, or Remain Stable (1)

• Population size governed by
• Births
• Deaths
• Immigration
• Emigration
• Population change
• (births immigration) (deaths
  emigration)

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Populations Can Grow, Shrink, or Remain Stable (2)

• Environmental resistance
• All factors that act to limit the growth of a
  population
• Carrying capacity
• Maximum population a given habitat can sustain

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Populations Can Grow, Shrink, or Remain Stable (3)

• Intrinsic rate of increase
• Rate at which population grows with unlimited
  resources
• Exponential growth
• Starts slowly, then accelerates to carrying
  capacity when meets environmental resistance
• Logistic growth
• Decreased population growth rate as population
  size reaches carrying capacity

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Exponential Growth to Carrying Capacity
Fig. 4-7, p. 77
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Logistic Growth of Sheep in Tasmania
Fig. 4-8, p. 77
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Population overshoots carrying capacity
Carrying capacity
Population recovers and stabilizes
Population runs out of resources and crashes
Exponential growth
Fig. 4-8, p. 77
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Carrying capacity
Population recovers and stabilizes
Exponential growth
Stepped Art
Fig. 4-8, p. 77
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When a Population Exceeds Its Habitats Carrying
Capacity, Its Population Can Crash

• A population exceeds the areas carrying capacity
• Reproductive time lag may lead to overshoot
• Population crash
• Damage may reduce areas carrying capacity

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Exponential Growth, Overshoot, and Population
Crash of a Reindeer
Fig. 4-9, p. 78
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Population overshoots carrying capacity
Population crashes
Carrying capacity
Fig. 4-9, p. 78
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Carrying capacity
Stepped Art
Fig. 4-9, p. 78
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Species Have Different Reproductive Patterns (1)

• Some species are opportunists
• Many, usually small, offspring
• Little or no parental care
• Massive deaths of offspring
• Insects, bacteria, algae

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Species Have Different Reproductive Patterns (2)

• Other species are competitor species
• Reproduce later in life
• Small number of offspring with long life spans
• Young offspring grow inside mother
• Long time to maturity
• Protected by parents, and potentially groups
• Humans
• Elephants

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4-5 What Factors Influence the Size of the Human
Population?

• Concept 4-5A Population size increases because
  of births and immigration and decreases through
  deaths and emigration.
• Concept 4-5B The average number of children born
  to women in a population (total fertility rate)
  is the key factor that determines population
  size.
• Concept 4-5C The numbers of males and females in
  young, middle, and older age groups determine how
  fast a population grows or declines.

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Human Population Growth Continues but It Is
Unevenly Distributed (1)

• Reasons for human population increase
• Movement into new habitats and climate zones
• Early and modern agriculture methods
• Control of infectious diseases through
• Sanitation systems
• Antibiotics
• Vaccines
• Health care
• Most population growth over last 100 years due to
  drop in death rates

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Human Population Growth Continues but It Is
Unevenly Distributed (2)

• Population growth in developing countries is
  increasing 9 times faster than developed
  countries
• 2050
• 95 of growth in developing countries
• 7.8-10.8 billion people
• Should the optimum sustainable population be
  based on cultural carrying capacity?

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Annual Growth Rate of Five Most Populous
Countries, 1950-2010
Fig. 4-10, p. 80
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The Human Population Can Grow, Decline, or Remain
Fairly Stable

• Population change
• Births fertility
• Deaths mortality
• Migration
• Population change
• (births immigration) (deaths emigration)
• Crude birth rate live births/1000/year
• Crude death rate deaths/1000/year

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Women Having Fewer Babies but Not Few Enough to
Stabilize the Worlds Population

• Fertility rate
• number of children born to a woman during her
  lifetime
• Replacement-level fertility rate
• Average number of children a couple must have to
  replace themselves
• 2.1 in developed countries
• Up to 2.5 in developing countries
• Total fertility rate (TFR)
• Average number of children born to women in a
  population

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Case Study The U.S. Population Is Growing Rapidly

• Population still growing and not leveling off
• 76 million in 1900
• 310 million in 2010
• Drop in TFR in U.S.
• Rate of population growth has slowed
• Changes in lifestyle in the U.S. during the 20th
  century

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U.S. TFRs and birth rates 1917-2010
Fig. 4-11, p. 81
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20th Century Lifestyle Changes in the U.S.

Fig. 4-12, p. 81
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Several Factors Affect Birth Rates and Fertility
Rates (1)

• Children as part of the labor force
• Cost of raising and educating children
• Availability of private and public pension
• Urbanization
• Educational and employment opportunities for
  women

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Several Factors Affect Birth Rates and Fertility
Rates (2)

• Average age of a woman at birth of first child
• Availability of legal abortions
• Availability of reliable birth control methods
• Religious beliefs, traditions, and cultural norms

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Several Factors Affect Death Rates (1)

• Life expectancy
• Infant mortality rate
• Number of live births that die in first year
• Why are people living longer?
• Increased food supply and distribution
• Better nutrition
• Medical advances
• Improved sanitation

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Several Factors Affect Death Rates (2)

• U.S. is 54th in world for infant mortality rate
• U.S. infant mortality rate high due to
• Inadequate health care for poor women during
  pregnancy and their infants
• Drug addiction among pregnant women
• High birth rate among teenagers

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Migration Affects an Areas Population Size

• Economic improvement
• Religious freedom
• Political freedom
• Wars
• Environmental refugees

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Case Study The United States A Nation of
Immigrants

• Historical role of immigration in the U.S.
• Legal immigration
• Illegal immigration
• Controversy over immigration policy

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Legal Immigration to the U.S. between 1820 and
2006

Fig. 4-13, p. 83
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1907
1914 New laws restrict immigration
Great Depression
Fig. 4-13, p. 83
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A Populations Age Structure Helps Us Make
Projections

• Age structure categories
• Prereproductive ages (0-14)
• Reproductive ages (15-44)
• Postreproductive ages (45 and older)
• Seniors are the fastest-growing age group

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Generalized Population Age-Structure Diagrams

Fig. 4-14, p. 84
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Case Study The American Baby Boom

• 79 million people, 36 of adults
• Affect politics and economics
• Now becoming senior citizens
• Graying of America

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Tracking the Baby-Boom Generation in the United
States

Fig. 4-15, p. 84
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Populations Made Up of Mostly Older People Can
Decline Rapidly

• Slow decline
• Manageable
• Rapid decline
• Severe economic problems
• How pay for services for elderly
• Proportionally fewer young people working
• Labor shortages
• Severe social problems

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Some Problems with Rapid Population Decline

Fig. 4-16, p. 85
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Populations Can Decline from a Rising Death Rate
The AIDS Tragedy

• 27 million killed 1981-2009
• Many young adults die loss of most productive
  workers
• Sharp drop in life expectancy
• International community
• Reduce the spread of HIV through education and
  health care
• Financial assistance and volunteers

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4-6 How Can We Slow Human Population Growth?

• Concept 4-6 We can slow human population growth
  by reducing poverty, elevating the status of
  women, and encouraging family planning.

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As Countries Develop, Their Populations Tend to
Grow More Slowly

• Demographic transition
• First death rates decline
• Then birth rates decline
• Four stages
• Preindustrial
• Transitional
• Industrial
• Postindustrial

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Four Stages of the Demographic Transition

Fig. 4-17, p. 87
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Empowering Women Can Slow Population Growth

• Factors that decrease total fertility rates
• Education
• Paying jobs
• Ability to control fertility
• Women
• Do most of the domestic work and child care
• Provide unpaid health care
• 2/3 of all work for 10 of worlds income
• Discriminated against legally and culturally

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Planning For Babies Works

• Family planning in less-developed countries
• Responsible for a 55 drop in TFRs
• Financial benefits money spent on family
  planning saves far more in health, education
  costs
• Two problems
• 42 pregnancies unplanned, 26 end with abortion
• Many couples do not have access to family
  planning

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Case Study Slowing Population Growth in China
A Success Story

• 1.3 billion people
• Promotes one-child families
• Contraception, abortion, sterilization
• Fast-growing economy
• Serious resource and environmental problems

85
Case Study Slowing Population Growth in India

• 1.2 billion people, most populous country in 2015
• Problems
• Poverty
• Malnutrition
• Environmental degradation
• Bias toward having male children
• Poor couples want many children
• Only 48 of couples use family planning

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Demographic Data for India and China
Fig. 4-18, p. 88
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It Is Possible to Reduce Population Growth

1. Access to family planning and reproductive health
   care
2. Improve health care for pregnant women and
   infants
3. Implement national population policies
4. Improve the status of women
5. Increase the involvement of men in child-rearing
6. Reduce poverty
7. Reduce unsustainable patterns of production and
   consumption

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Three Big Ideas

1. Each species plays a specific ecological role in
   the ecosystem where it is found (ecological
   niche).
2. Certain interactions among species, along with
   other natural limits to population growth in
   nature, affect the resource use and population
   sizes of all species, including humans.

89
Three Big Ideas

1. We can slow population growth by reducing poverty
   through economic development, elevating the
   status of women, and encouraging family planning.